Positive resist composition and patterning process

ABSTRACT

A positive resist composition comprising a polymer having carboxyl groups substituted with an acid labile group having formula (1) exhibits a high contrast of alkaline dissolution rate before and after exposure, a high resolution, a reduced acid diffusion rate, and forms a pattern with good profile, minimal edge roughness, and etch resistance. In formula (1), R 1  is methylene or ethylene, R 2  is alkyl, aryl, or alkenyl, which may contain oxygen or sulfur, R 3  is fluorine or trifluoromethyl, and m is an integer of 1 to 4.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2011-218939 filed in Japan on Oct. 3, 2011,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a positive resist composition, and moreparticularly to a chemically amplified positive resist compositioncomprising a specific polymer; and a patterning process using the same.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, extreme ultraviolet (EUV)lithography of 13.5 nm wavelength, and double patterning version of theArF lithography, on which active research efforts have been made.

With respect to high-energy radiation of very short wavelength such aselectron beam (EB) or x-ray, hydrocarbons and similar light elementsused in resist materials have little absorption. Then polyhydroxystyrenebase resist materials are under consideration. Resist materials for EBlithography are practically used in the mask image writing application.Recently, the mask manufacturing technology becomes of greater interest.Reduction projection exposure systems or steppers have been used sincethe time when the exposure light was g-line. While their demagnificationfactor was ⅕, a factor of ¼ is now used as a result of chip sizeenlargement and projection lens diameter increase. It becomes of concernthat a dimensional error of a mask has an impact on the dimensionalvariation of a pattern on wafer. It is pointed out that as the patternfeature is reduced, the value of a dimensional variation on the waferbecomes greater than the value of a dimensional error of the mask. Thisis evaluated by a mask error enhancement factor (MEEF) which is adimensional variation on wafer divided by a dimensional error of mask.Patterns on the order of 45 nm often show an MEEF in excess of 4. In asituation including a demagnification factor of ¼ and a MEEF of 4, themask manufacture needs an accuracy substantially equivalent to that forequi-magnification masks.

The exposure system for mask manufacturing made a transition from thelaser beam exposure system to the EB exposure system to increase theaccuracy of line width. Since a further size reduction becomes possibleby increasing the accelerating voltage of the electron gun in the EBexposure system, the accelerating voltage increased from 10 keV to 30keV and reached 50 keV in the current mainstream system, with a voltageof 100 keV being under investigation.

As the accelerating voltage increases, a lowering of sensitivity ofresist film becomes of concern. As the accelerating voltage increases,the influence of forward scattering in a resist film becomes so reducedthat the contrast of electron image writing energy is improved toameliorate resolution and dimensional control whereas electrons can passstraightforward through the resist film so that the resist film becomesless sensitive. Since the mask exposure tool is designed for exposure bydirect continuous writing, a lowering of sensitivity of resist filmleads to an undesirably reduced throughput. Due to a need for highersensitivity, chemically amplified resist compositions are contemplated.

Thinning of resist film is in progress to facilitate reduction ofpattern feature in the EB lithography for mask manufacturing and toprevent the pattern from collapsing due to a higher aspect ratio duringdevelopment. In the case of photolithography, a thinning of resist filmgreatly contributes to resolution improvement. This is becauseintroduction of chemical mechanical polishing (CMP) or the like hasdriven forward device planarization. In the case of mask manufacture,substrates are flat, and the thickness of processable substrates (e.g.,Cr, MoSi or SiO₂) is predetermined by a percent light shield or phaseshift control. The dry etch resistance of resist film must be improvedbefore the film can be reduced in thickness.

It is generally believed that there is a correlation between the carbondensity and the dry etching resistance of resist film. For EB writingwhich is not affected by absorption, resist materials based on novolacresins having better etching resistance have been developed. Indenecopolymers described in Patent Document 1 and acenaphthylene copolymersdescribed in Patent Document 2 are expected to have improved etchingresistance due to a high carbon density and a robust main chainstructure based on cycloolefin structure.

Also, with respect to the soft x-ray (EUV) lithography at wavelength5-20 nm, the reduced absorption of carbon atoms was reported. Increasingthe carbon density is effective not only for improving dry etchingresistance, but also for increasing the transmittance in the soft x-raywavelength region.

As the feature size is reduced, image blurs due to acid diffusion becomea problem. To insure resolution for fine patterns with a size of 45 nmet seq., not only an improvement in dissolution contrast is requisite,but control of acid diffusion is also important, as known from previousreports. Since chemically amplified resist compositions are designedsuch that sensitivity and contrast are enhanced by acid diffusion, anattempt to minimize acid diffusion by reducing the temperature and/ortime of post-exposure baking (PEB) fails, resulting in drasticreductions of sensitivity and contrast. Since the distance of aciddiffusion is closely related to the type of acid labile group, it wouldbe desirable to have an acid labile group which permits deprotectionreaction to proceed at a very short distance of acid diffusion.

In Patent Document 3, methacrylates having an indane, acenaphthene,fluorene or 9,10-dihydroanthracene pendant are exemplified as themonomer to form a copolymer for use in photoresist underlayer formingmaterial. Acid labile groups in the form of 1-indane or1-tetrahydronaphthalene(meth)acrylate are proposed. Inclusion ofaromatic within the acid labile group improves etch resistance and EUVtransmittance. Patent Document 4 discloses a resist material comprisinga copolymer of hydroxystyrene wherein an ester bond moiety is secondaryor tertiary. In particular, 1-indane and 1-tetrahydronaphthalene of thesecondary ester require a high level of activation energy fordeprotection and suffer a dimensional change with a change of PEBtemperature, that is, a dimensional difference dependent on PEBtemperature. On the other hand, 1-indane and 1-tetrahydronaphthalene ofthe tertiary ester have a very low level of activation energy and lowheat resistance so that deprotection reaction may take place by the heatduring polymerization.

Proposed as protective groups of aromatic-containing dimethylcarbinoltype are dimethylbenzene (Patent Document 5), dimethylnaphthalene(Patent Document 6), and acid labile groups of tertiary ester such asaromatic-containing carbinol ester or methylindane (Patent Document 7).These acid labile groups are highly susceptible to deprotection becausethe group of benzyl cation type resulting from deprotection is verystable, but have low thermal stability, extreme sensitivity to acid,inability to control acid diffusion, and low maximum resolution.

To overcome the drawback of aromatic-containing dimethylcarbinol typeprotective groups being susceptible to deprotection, Patent Document 8proposes secondary aromatic-containing groups. However, the secondaryacid labile groups are unsusceptible to deprotection and have a narrowPEB temperature margin, as compared with the tertiary carbinol typeprotective groups. While the aromatic-containing acid labile groups havethe advantage of improved etch resistance, it is still desired todevelop an acid labile group having high thermal stability andappropriate deprotection reactivity.

A tradeoff among sensitivity, edge roughness and resolution is reported.Increasing sensitivity leads to reductions of edge roughness andresolution. Controlling acid diffusion improves resolution at thesacrifice of edge roughness and sensitivity. Addition of an acidgenerator capable of generating a bulky acid is effective forsuppressing acid diffusion, but leads to reductions of edge roughnessand sensitivity as pointed out above. It is then proposed tocopolymerize a polymer with an acid generator in the form of an oniumsalt having polymerizable olefin. Patent Documents 9 to 11 disclosesulfonium salts having polymerizable olefin capable of generating asulfonic acid and similar iodonium salts. A photoresist using a basepolymer having a polymerizable acid generator copolymerized thereinexhibits reduced edge roughness due to controlled acid diffusion anduniform dispersion of acid generator within the polymer, succeeding inimproving both resolution and edge roughness at the same time.

CITATION LIST

-   Patent Document 1: JP 3865048-   Patent Document 2: JP-A 2006-169302-   Patent Document 3: JP-A 2007-171895-   Patent Document 4: JP-A 2007-279699-   Patent Document 5: JP 3438103-   Patent Document 6: JP-A 2011-123463-   Patent Document 7: JP-A 2010-122579-   Patent Document 8: JP-A 2008-096951-   Patent Document 9: JP-A H04-230645-   Patent Document 10: JP-A 2005-084365-   Patent Document 11: JP-A 2006-045311

DISCLOSURE OF INVENTION

An object of the present invention is to provide a positive resistcomposition, typically chemically amplified positive resist composition,comprising a specific polymer, which exhibits a high resolutionsurpassing prior art positive resist compositions, and forms a resistfilm having a minimal edge roughness (LER or LWR), a good patternprofile after exposure, and improved etch resistance. Another object isto provide a pattern forming process using the same.

Making investigations to seek for a positive resist composition whichexhibits a high resolution, a minimal edge roughness (LER or LWR), agood pattern profile after exposure and development, and improved etchresistance, the inventors have found that better results are obtainedwhen a polymer comprising recurring units having a fluorinated indane ortetrahydronaphthalene-containing tertiary ester, specifically selectedfrom (meth)acrylic acid and derivatives thereof, styrenecarboxylic acid,and vinylnaphthalenecarboxylic acid, is used as a base resin toformulate a positive resist composition, typically chemically amplifiedpositive resist composition.

As alluded to previously, acid labile groups in the form of indane ortetrahydronaphthalene-containing tertiary esters require very lowactivation energy for acid-catalyzed deprotection reaction as comparedwith acid labile groups in the form of tertiary alkyl groups, so thatdeprotection reaction may take place even at temperatures as low as 50°C. If a polymer having an acid labile group having too low activationenergy for deprotection reaction is used as a base resin in resistmaterial, too low a PEB temperature interferes with consistenttemperature control and makes control of acid diffusion difficult. Ifthe acid diffusion distance is uncontrollable, the pattern afterdevelopment is degraded in CD uniformity and maximum resolution. Anappropriate PEB temperature is necessary for the control of aciddiffusion, with a PEB temperature in the range of 80 to 100° C. beingappropriate.

Another problem arising from the use of low activation energy protectivegroups is that when a photoacid generator (PAG) is copolymerized into apolymer, the protective group may be eliminated during polymerization.While PAGs of onium salts are essentially neutral, the onium salt can bepartially dissociated by the heat during polymerization, or theprotective group can be deprotected by the heat during polymerization.Particularly when low activation energy protective groups are used,outstanding deprotection takes place during polymerization.

The acid labile groups in the form of indane ortetrahydronaphthalene-containing tertiary esters have the advantage ofexcellent etch resistance because of inclusion of benzene ring, but thedisadvantage that when a PAG is copolymerized, elimination of the acidlabile group occurs during polymerization. The attachment of an electronattractive group to benzene ring increases the activation energy fordeprotection. This is presumably because the electron attractive groupcauses to reduce the stability of a benzyl cation as intermediate in thecourse of deprotection. If an electron attractive group is attached to aprotective group which is extremely susceptible to deprotection, thenthe reactivity of deprotection reaction can be reduced to an optimumlevel.

It is generally believed that fluorine atoms have high absorptionrelative to EUV of 13.5 nm wavelength and thus exert a sensitizing orsensitivity enhancing effect. It is thus expected that sensitivity isimproved by introducing fluorine into the protective group. However, iffluorine is introduced into the acid labile group in the form oftertiary alkyl group, the stability of an intermediate cation ofdeprotection reaction is substantially reduced by the electronattracting effect of fluorine, and as a consequence, neither olefinformation nor deprotection reaction occurs. However, a tertiary acidlabile group having a fluorinated aromatic group exhibits appropriatereactivity for deprotection because the intermediate cation has optimumstability.

The above-specified polymer is used as a base resin in a positive resistcomposition, especially chemically amplified positive resist compositionfor the purposes of suppressing acid diffusion and improving dissolutioncontrast and etch resistance. Then the composition forms a resist filmwhich exhibits a remarkably high contrast of alkaline dissolution ratebefore and after exposure, a significant effect of suppressing aciddiffusion, a high resolution, a pattern of good profile and minimal edgeroughness after exposure, and improved etch resistance. The compositionis best suited as a fine pattern-forming material for the fabrication ofVLSIs and photomasks.

The positive resist composition forms a resist film which has a highdissolution contrast due to optimum deprotection reaction, effectivesuppression of acid diffusion, a high resolution, exposure latitude,process adaptability, a pattern of good profile after exposure, andimproved etch resistance. By virtue of these advantages, the compositionis fully useful in commercial application and is best suited as a maskpattern-forming material for the fabrication of VLSIs.

In one aspect, the invention provides a positive resist compositioncomprising as a base resin a polymer having carboxyl groups whosehydrogen is substituted by an acid labile group having the generalformula (1).

Herein R⁴ is methylene or ethylene, R² is a straight, branched or cyclicC₁-C₈ alkyl, C₆-C₁₀ aryl, or C₂-C₁₀ alkenyl group, which may contain anoxygen or sulfur atom, R³ is fluorine or trifluoromethyl, and m is aninteger of 1 to 4.

In a preferred embodiment, the polymer comprises recurring units (a) ofthe general formula (2), selected from (meth)acrylic acid andderivatives thereof, styrenecarboxylic acid, andvinylnaphthalenecarboxylic acid, each having substituted thereon an acidlabile group of formula (1), the polymer having a weight averagemolecular weight of 1,000 to 500,000.

Herein R¹ to R³, and m are as defined above, X¹ is a single bond,—C(═O)—O—R⁵—, phenylene or naphthylene group, R⁵ is a straight, branchedor cyclic C₁-C₁₀ alkylene group which may have an ester radical, etherradical or lactone ring, and R⁴ is hydrogen or methyl.

In a preferred embodiment, the polymer is a copolymer comprisingrecurring units (a) of the general formula (2), selected from(meth)acrylic acid and derivatives thereof, styrenecarboxylic acid, andvinylnaphthalenecarboxylic acid, each having substituted thereon an acidlabile group of formula (1), and recurring units (b) having an adhesivegroup selected from the class consisting of hydroxyl, lactone, ether,ester, carbonyl, cyano, sulfonic acid ester, sulfonamide groups, cyclic—O—C(═O)—S— and —O—C(═O)—NH— groups, molar fractions “a” and “b” of therespective units being in the range: 0<a<1.0, 0<b<1.0, and 0.05≦a+b≦1.0,the copolymer having a weight average molecular weight of 1,000 to500,000.

More preferably, the recurring units (b) are recurring units having aphenolic hydroxyl group. Even more preferably, the recurring unitshaving a phenolic hydroxyl group are selected from units (b1) to (b9)represented by the following general formula (3).

Herein Y¹, Y² and Y⁵ each are a single bond or —C(═O)—O—R²¹—, Y³ and Y⁴each are —C(═O)—O—R²²—, R²¹ and R²² each are a single bond or astraight, branched or cyclic C₁-C₁₀ alkylene group which may contain anether or ester radical, R²⁰ is each independently hydrogen or methyl, Z¹and Z² each are methylene or ethylene, Z³ is methylene, oxygen orsulfur, Z⁴ and Z⁵ each are CH or nitrogen, and p is 1 or 2.

In a preferred embodiment, the copolymer has further copolymerizedtherein recurring units selected from units (c1) to (c5) of indene,acenaphthylene, chromone, coumarin, and norbornadiene, or derivativesthereof, represented by the following general formula (4).

Herein R²³ to R²⁷ are each independently selected from the classconsisting of hydrogen, C₁-C₃₀ alkyl, partially or entirelyhalo-substituted alkyl, alkoxy, alkanoyl or alkoxycarbonyl group, C₆-C₁₀aryl group, halogen, and 1,1,1,3,3,3-hexafluoro-2-propanol, and W¹ ismethylene, oxygen or sulfur.

In a preferred embodiment, the copolymer has further copolymerizedtherein units selected from sulfonium salts (d1) to (d3) represented bythe following general formula (5) in addition to recurring units (a) and(b).

Herein R³⁰, R³⁴, and R³⁸ each are hydrogen or methyl, R³¹ is a singlebond, phenylene, —O—R⁴²—, or —C(═O)—Y¹⁰—R⁴²—, Y¹⁰ is oxygen or NH, R⁴²is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylene orphenylene group, which may contain a carbonyl, ester, ether or hydroxylradical, R³², R³³, R³⁵, R³⁶, R³⁷, R³⁹, R⁴⁰, and R⁴¹ are eachindependently a straight, branched or cyclic C₁-C₁₂ alkyl group whichmay contain a carbonyl, ester or ether radical, or a C₆-C₁₂ aryl, C₇-C₂₀aralkyl, or thiophenyl group, Z¹⁰ is a single bond, methylene, ethylene,phenylene, fluorophenylene, —O—R⁴³—, or —C(═O)—Z¹¹—R⁴³—, Z¹¹ is oxygenor NH, R⁴³ is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene or phenylene group, which may contain a carbonyl, ester,ether or hydroxyl radical, M⁻ is a non-nucleophilic counter ion, d1, d2and d3 are in the range of 0≦d1≦0.3, 0≦d2≦0.3, 0≦d3≦0.3, and0<d1+d2+d3≦0.3.

The resist composition may further comprise an organic solvent and anacid generator, the composition being a chemically amplified positiveresist composition. The resist composition may further comprise adissolution regulator, a basic compound, and/or a surfactant.

In another aspect, the invention provides a pattern forming processcomprising the steps of applying the positive resist composition definedabove onto a substrate to form a coating, baking, exposing tohigh-energy radiation, and developing the exposed coating in adeveloper.

The positive resist composition, typically chemically amplified positiveresist composition is used not only in the lithography for formingsemiconductor circuits, but also in the formation of mask circuitpatterns, micromachines, and thin-film magnetic head circuits.

ADVANTAGEOUS EFFECTS OF INVENTION

The positive resist composition exhibits a remarkably high contrast ofalkaline dissolution rate before and after exposure, a high resolution,a good pattern profile and minimal edge roughness (LER or LWR) afterexposure, a significant effect of suppressing acid diffusion rate, andimproved etch resistance. The composition is thus suited as a finepattern-forming material for the fabrication of VLSIs or photomasks anda pattern-forming material for EUV lithography.

DESCRIPTION OF EMBODIMENTS

The singular forms “a,” an and the include plural referents unless thecontext clearly dictates otherwise. “Optional” or “optionally” meansthat the subsequently described event or circumstances may or may notoccur, and that description includes instances where the event orcircumstance occurs and instances where it does not.

As used herein, the terminology “(meth)acrylic acid” or “(meth)acrylate”refers collectively to acrylic and methacrylic acid or acrylate andmethacrylate. The terminology “C_(x)-C_(y)”, as applied to a particularunit, such as, for example, a chemical compound or a chemicalsubstituent group, means having a carbon atom content of from “x” carbonatoms to “y” carbon atoms per such unit.

The abbreviations have the following meaning.

EB: electron beamEUV: extreme ultravioletPAG: photoacid generatorPEB: post-exposure bakeLER: line edge roughnessLWR: line width roughnessMw: weight average molecular weightMn: number average molecular weightMw/Mn: dispersity or average molecular weight distributionGPC: gel permeation chromatography

The invention provides a positive resist composition comprising as abase resin a polymer or high-molecular-weight compound having carboxylgroups whose hydrogen is substituted by an acid labile group having thegeneral formula (1).

Herein R¹ is methylene or ethylene, R² is a straight, branched or cyclicC₁-C₈ alkyl, C₆-C₁₀ aryl, or C₂-C₁₀ alkenyl group, which may contain anoxygen or sulfur atom, R³ is fluorine or trifluoromethyl, and m is aninteger of 1 to 4.

Examples of R² include methyl, ethyl, propyl, butyl, cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, oxonorbornyl, vinyl,allyl, propenyl, ethynyl, propynyl, thienyl, and furyl.

In a preferred embodiment, the acid labile group of formula (1)substitutes for hydrogen atom of the carboxyl group on (meth)acrylicacid and derivatives thereof, styrenecarboxylic acid, andvinylnaphthalenecarboxylic acid. It is noted that (meth)acrylic acid andderivatives thereof are collectively referred to as (meth)acrylates,hereinafter. Specifically, a polymer comprising recurring units (a) ofthe general formula (2) and having a weight average molecular weight(Mw) of 1,000 to 500,000 is used as the base resin.

Herein R¹ to R³, and m are as defined above, X¹ is a single bond,—C(═O)—O—R⁵—, phenylene or naphthylene group, R⁵ is a straight, branchedor cyclic C₁-C₁₀ alkylene group which may have an ester (—COO—) radical,ether (—O—) radical or lactone ring, and R⁴ is hydrogen or methyl.

Typical of the C₁-C₁₀ alkylene group having lactone ring is a group ofthe formula below.

Specifically, the recurring units (a) of formula (2) include units (a-1)to (a-4) represented by the following formula (6).

Herein, R¹ to R⁵, and m are as defined above.

In particular, these acid labile groups are applicable to the KrF, EBand EUV lithography.

Examples of suitable monomers from which recurring units (a-1) to (a-4)are derived are shown below.

The polymerizable, acid-labile ester compounds from which recurringunits (a) are derived may be prepared, for example, by reaction of afluoroalkylindanol with methacrylic acid chloride.

In a preferred embodiment, the polymer having acid labile groups offormula (1) is a copolymer comprising recurring units (a) of formula(2), selected from (meth)acrylates, styrenecarboxylic acid, andvinylnaphthalenecarboxylic acid, and recurring units (b) having anadhesive group selected from among hydroxyl, lactone, ether, ester,carbonyl, cyano, sulfonic acid ester, sulfonamide groups, cyclic—O—C(═O)—S— and —O—C(═O)—NH— groups. More preferably, the recurringunits (b) are recurring units having a phenolic hydroxyl group becausethe group has a sensitizing effect in the EB and EUV lithography. Therecurring units having a phenolic hydroxyl group are preferably selectedfrom units (b1) to (b9) represented by the following general formula(3).

Herein Y¹, Y² and Y⁵ each are a single bond or —C(═O)—O—R²¹—, Y³ and Y⁴each are —C(═O)—O—R²²—, R²¹ and R²² each are a single bond or astraight, branched or cyclic C₁-C₁₀ alkylene group which may contain anether or ester radical, R²⁰ is each independently hydrogen or methyl, Z¹and Z² each are methylene or ethylene, Z³ is methylene, oxygen atom orsulfur atom, Z⁴ and Z⁵ each are CH or nitrogen atom, and p is 1 or 2.

Examples of suitable monomers from which the recurring units (b1) to(b9) having a phenolic hydroxyl group are derived are given below.

Examples of suitable monomers from which the recurring units (b) havingan adhesive group selected from among non-phenolic hydroxyl group,lactone ring, ether group, ester group, carbonyl group, cyano group,sulfonic acid ester group, sulfonamide group, cyclic —O—C(═O)—S— and—O—C(═O)—NH— group are derived are given below.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxy group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

In a more preferred embodiment, the copolymer has further copolymerizedtherein recurring units (c) selected from units (c1) to (c5) of indene,acenaphthylene, chromone, coumarin, and norbornadiene, or derivativesthereof, represented by the following formula (4).

Herein R²³ to R²⁷ are each independently hydrogen, a C₁-C₃₀ alkyl,haloalkyl, alkoxy, alkanoyl or alkoxycarbonyl group, C₆-C₁₀ aryl group,halogen, or 1,1,1,3,3,3-hexafluoro-2-propanol group, and W¹ ismethylene, oxygen or sulfur. As used herein, the term “haloalkyl” refersto alkyl in which some or all hydrogen atoms are substituted by halogen.

Examples of suitable monomers from which recurring units (c1) to (c5) ofindene, acenaphthylene, chromone, coumarin, and norbornadienederivatives are derived are given below.

In a further embodiment, an acid generator (d) in the form of an oniumsalt having polymerizable olefin may be copolymerized with the foregoingmonomers. JP-A H04-230645, JP-A 2005-084365, and JP-A 2006-045311disclose sulfonium salts having polymerizable olefin capable ofgenerating a specific sulfonic acid and similar iodonium salts. JP-A2006-178317 discloses a sulfonium salt having sulfonic acid directlyattached to the main chain.

In this embodiment, the copolymer may have further copolymerized thereinrecurring units (d1) to (d3) having a sulfonium salt, represented by thefollowing formula (5). Sometimes, units (d1) to (d3) are collectivelyreferred to as units (d).

Herein R³⁰, R³⁴, and R³⁸ each are hydrogen or methyl. R³¹ is a singlebond, phenylene, —O—R⁴²—, or —C(═O)—Y¹⁰—R⁴²—, wherein Y¹⁰ is oxygen orNH, and R⁴² is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene or phenylene group, which may contain a carbonyl (—CO—),ester (—COO—), ether (—O—) or hydroxyl radical. R³², R³³, R³⁵, R³⁶, R³⁷,R³⁹, R⁴⁰, and R⁴¹ are each independently a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain a carbonyl, ester or ether radical,or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenyl group. Z¹⁰ is a singlebond, methylene, ethylene, phenylene, fluorophenylene, —O—R⁴³—, or—C(═O)—Z¹¹—R⁴³—, wherein Z¹¹ is oxygen or NH, and R⁴³ is a straight,branched or cyclic C₁-C₆ alkylene group, alkenylene or phenylene group,which may contain a carbonyl, ester, ether or hydroxyl radical. M⁻ is anon-nucleophilic counter ion. Molar fractions d1, d2 and d3 are in therange of 0≦d1≦0.3, 0≦d2≦0.3, 0≦d3≦0.3, and 0≦d (=d1+d2+d3) 0.3.

Examples of the non-nucleophilic counter ion represented by M⁻ includehalide ions such as chloride and bromide ions; fluoroalkylsulfonate ionssuch as triflate, 1,1,1-trifluoroethanesulfonate, andnonafluorobutanesulfonate; arylsulfonate ions such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate, and1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such asmesylate and butanesulfonate; imidates such asbis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide andbis(perfluorobutylsulfonyl)imide; methidates such astris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

The attachment of an acid generator to the polymer main chain iseffective in restraining acid diffusion, thereby preventing a reductionof resolution due to blur by acid diffusion. Also edge roughness (LER orLWR) is improved since the acid generator is uniformly dispersed.

While the polymer according to the invention comprises acid labilegroup-substituted recurring units (a) as essential units, it may haveadditionally copolymerized therein recurring units (e) of (meth)acrylatehaving substituted thereon an acid labile group R¹⁵ and/or recurringunits (f) of hydroxystyrene having substituted thereon an acid labilegroup R¹⁷, as represented by the following general formula (7).

Herein R¹⁴ and R¹⁶ each are hydrogen or methyl, R¹⁵ and R¹⁷ each are anacid labile group other than formula (1), Z is a single bond, ester oramide group, and q is 1 or 2.

Besides the recurring units (a) to (f), additional recurring units (g)may be copolymerized in the polymer, which include recurring unitsderived from styrene, vinylnaphthalene, vinylanthracene, vinylpyrene,methyleneindane, and the like.

The acid labile groups represented by R¹⁵ and R¹⁷ in formula (7) may beselected from a variety of such groups. The acid labile groups may bethe same or different and preferably include groups of the followingformulae (A-1) to (A-3).

In formula (A-1), R^(L30) is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in whicheach alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (A-3). Exemplary tertiary alkylgroups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxolan-5-yl. Letter A1 is an integer of 0 to 6.

In formula (A-2), R^(L31) and R^(L32) are hydrogen or straight, branchedor cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms. Exemplary alkyl groups include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl,2-ethylhexyl, and n-octyl. R^(L33) is a monovalent hydrocarbon group of1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may containa heteroatom such as oxygen, examples of which include straight,branched or cyclic alkyl groups and substituted forms of such alkylgroups in which some hydrogen atoms are replaced by hydroxyl, alkoxy,oxo, amino, alkylamino or the like. Illustrative examples of thesubstituted alkyl groups are shown below.

A pair of R^(L31) and R^(L32), R^(L31) and R^(L33), or R^(L32) andR^(L33) may bond together to form a ring with the carbon and oxygenatoms to which they are attached. Each of R^(L31), R^(L32) and R^(L33)is a straight or branched alkylene group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms when they form a ring, while the ringpreferably has 3 to 10 carbon atoms, more preferably 4 to 10 carbonatoms.

Examples of the acid labile groups of formula (A-1) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl groups.

Also included are substituent groups having the formulae (A-1)-1 to(A-1)-10.

Herein R^(L37) is each independently a straight, branched or cyclicC₁-C₁₀ alkyl group or C₆-C₂₀ aryl group. R^(L38) is hydrogen or astraight, branched or cyclic C₁-C₁₀ alkyl group. R^(L39) is eachindependently a straight, branched or cyclic C₂-C₁₀ alkyl group orC₆-C₂₀ aryl group. A1 is an integer of 0 to 6.

Of the acid labile groups of formula (A-2), the straight and branchedones are exemplified by the following groups having formulae (A-2)-1 to(A-2)-35.

Of the acid labile groups of formula (A-2), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Other examples of acid labile groups include those of the followingformula (A-2a) or (A-2b) while the polymer may be crosslinked within themolecule or between molecules with these acid labile groups.

Herein R^(L40) and R^(L41) each are hydrogen or a straight, branched orcyclic C₁-C₈ alkyl group, or R^(L40) and R^(L41), taken together, mayform a ring with the carbon atom to which they are attached, and R^(L40)and R^(L41) are straight or branched C₁-C₈ alkylene groups when theyform a ring. R^(L42) is a straight, branched or cyclic C₁-C₁₀ alkylenegroup. Each of B1 and D1 is 0 or an integer of 1 to 10, preferably 0 oran integer of 1 to 5, and C1 is an integer of 1 to 7. “A” is a(C1+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group having 1 to 50 carbonatoms, which may be separated by a heteroatom or in which some hydrogenatoms attached to carbon atoms may be substituted by hydroxyl, carboxyl,carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or —NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkyltriyl and alkyltetrayl groups,and C₆-C₃₀ arylene groups, which may contain a heteroatom or in whichsome hydrogen atoms attached to carbon atoms may be substituted byhydroxyl, carboxyl, acyl groups or halogen atoms. The subscript C1 ispreferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (A-2a) and (A-2b) areexemplified by the following formulae (A-2)-36 through (A-2)-43.

In formula (A-3), R^(L34), R^(L35) and R^(L36) each are a monovalenthydrocarbon group, typically a straight, branched or cyclic C₁-C₂₀ alkylgroup, which may contain a heteroatom such as oxygen, sulfur, nitrogenor fluorine. A pair of R^(L34) and R^(L35), R^(L34) and R^(L36), orR^(L35) and R^(L36) may bond together to form a C₃-C₂₀ ring, typicallyalicyclic, with the carbon atom to which they are attached.

Exemplary tertiary alkyl groups of formula (A-3) include tert-butyl,triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, andtert-amyl.

Other exemplary tertiary alkyl groups include those of the followingformulae (A-3)-1 to (A-3)-18.

Herein R^(L43) is each independently a straight, branched or cyclicC₁-C₈ alkyl group or C₆-C₂₀ aryl group, typically phenyl or naphthyl,R^(L44) and R^(L46) each are hydrogen or a straight, branched or cyclicC₁-C₂₀ alkyl group, and R^(L45) is a C₆-C₂₀ aryl group, typicallyphenyl.

The polymer may be crosslinked within the molecule or between moleculeswith groups having R^(L47) which is a di- or multi-valent alkylene orarylene group, as shown by the following formulae (A-3)-19 and (A-3)-20.

Herein R^(L43) is as defined above, R^(L47) is a straight, branched orcyclic C₁-C₂₀ alkylene group or arylene group, typically phenylene,which may contain a heteroatom such as oxygen, sulfur or nitrogen, andE1 is an integer of 1 to 3.

Of recurring units having acid labile groups of formula (A-3), recurringunits of (meth)acrylate having an exo-form structure represented by theformula (A-3)-21 are preferred.

Herein, R¹⁴ is as defined above; R^(c3) is a straight, branched orcyclic C₁-C₈ alkyl group or an optionally substituted C₆-C₂₀ aryl group;R^(c4) to R^(c9), R^(c12) and R^(c13) are each independently hydrogen ora monovalent C₁-C₁₅ hydrocarbon group which may contain a heteroatom;and R^(c10) and R^(c11) are hydrogen or a monovalent C₁-C₁₅ hydrocarbongroup which may contain a heteroatom. Alternatively, a pair of R^(c4)and R^(c5), R^(c6) and R^(c8), R^(c6) and R^(c9), R^(c7) and R^(c9),R^(c7) and R^(c13), R^(c8) and R^(c12), R^(c10) and R^(c11), or R^(c11)and R^(c12), taken together, may form a ring, and in that event, eachring-forming R is a divalent C₁-C₁₅ hydrocarbon group which may containa heteroatom. Also, a pair of R^(c4) and R^(c13), R^(c10) and R^(c13),or R^(c6) and R^(c8) which are attached to vicinal carbon atoms may bondtogether directly to form a double bond. The formula also represents anenantiomer.

The ester form monomers from which recurring units having an exo-formstructure represented by formula (A-3)-21 are derived are described inU.S. Pat. No. 6,448,420 (JP-A 2000-327633). Illustrative non-limitingexamples of suitable monomers are given below.

Also included in the acid labile groups of formula (A-3) are acid labilegroups of (meth)acrylate having furandiyl, tetrahydrofurandiyl oroxanorbornanediyl as represented by the following formula (A-3)-22.

Herein, R¹⁴ is as defined above; R^(c14) and R^(c15) are eachindependently a monovalent, straight, branched or cyclic C₁-C₁₀hydrocarbon group, or R^(c14) and R^(c15), taken together, may form analiphatic hydrocarbon ring with the carbon atom to which they areattached. R^(c16) is a divalent group selected from furandiyl,tetrahydrofurandiyl and oxanorbornanediyl. R^(c17) is hydrogen or amonovalent, straight, branched or cyclic C₁-C₁₀ hydrocarbon group whichmay contain a heteroatom.

Examples of the monomers from which the recurring units substituted withacid labile groups having furandiyl, tetrahydrofurandiyl andoxanorbornanediyl are derived are shown below. Note that Me is methyland Ac is acetyl.

The polymer used herein may be synthesized by any desired methods, forexample, by dissolving one or more monomers selected from the monomersto form the recurring units (a) to (g) in an organic solvent, adding aradical polymerization initiator thereto, and effecting heatpolymerization. Examples of the organic solvent which can be used forpolymerization include toluene, benzene, tetrahydrofuran, diethyl etherand dioxane. Examples of the polymerization initiator used hereininclude 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, analternative method is possible. Specifically, acetoxystyrene oracetoxyvinylnaphthalene is used instead of hydroxystyrene orhydroxyvinylnaphthalene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis as mentioned above, for therebyconverting the polymer product to polyhydroxystyrene orhydroxypolyvinylnaphthalene. For alkaline hydrolysis, a base such asaqueous ammonia or triethylamine may be used. The reaction temperatureis −20° C. to 100° C., preferably 0° C. to 60° C., and the reaction timeis 0.2 to 100 hours, preferably 0.5 to 20 hours.

In the copolymer, recurring units (a) to (g) may be incorporated in thefollowing molar fraction:

0<a<1.0, preferably 0.1≦a≦0.9, and more preferably 0.15≦a≦0.8;0≦b<1.0, preferably 0.1≦b≦0.9, and more preferably 0.15≦b≦0.8;0≦c<1.0, preferably 0≦c≦0.9, and more preferably 0≦c≦0.8;

-   0≦d≦0.3, preferably 0≦d≦0.2, and more preferably 0≦d≦0.15;    0≦e≦0.5, preferably 0≦e≦0.4, and more preferably 0≦e≦0.3;    0≦f≦0.5, preferably 0≦f≦0.4, and more preferably 0≦f≦0.3;    0≦g≦0.5, preferably 0≦g≦0.4, and more preferably 0≦g≦0.3;    preferably 0.2≦a+b+c≦1.0, more preferably 0.3≦a+b+c≦1.0; and    a+b+c+d+e+f+g=1.

The meaning of a+b+c=1, for example, is that in a polymer comprisingrecurring units (a), (b), and (c), the sum of recurring units (a), (b),and (c) is 100 mol % based on the total amount of entire recurringunits. The meaning of a+b+c<1 is that the sum of recurring units (a),(b), and (c) is less than 100 mol % based on the total amount of entirerecurring units, indicating the inclusion of other recurring units.

The polymer serving as the base resin in the resist composition shouldpreferably have a weight average molecular weight (Mw) in the range of1,000 to 500,000, and more preferably 2,000 to 30,000, as measured byGPC versus polystyrene standards. With too low a Mw, the resistcomposition may become less heat resistant. A polymer with too high a Mwmay lose alkaline solubility and give rise to a footing phenomenon afterpattern formation.

If a multi-component polymer has a wide molecular weight distribution ordispersity (Mw/Mn), which indicates the presence of lower and highermolecular weight polymer fractions, there is a possibility that foreignmatter is left on the pattern or the pattern profile is degraded. Theinfluences of molecular weight and dispersity become stronger as thepattern rule becomes finer. Therefore, the multi-component copolymershould preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0,especially 1.0 to 1.5, in order to provide a resist composition suitablefor micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity is acceptable.

The polymer is advantageously used as a base resin in a positive resistcomposition, typically chemically amplified positive resist composition.Specifically, the polymer is used as a base resin and combined with anydesired components including an organic solvent, acid generator,dissolution regulator, basic compound, surfactant, and acetylene alcoholto formulate a positive resist composition. This positive resistcomposition has a very high sensitivity in that the dissolution rate indeveloper of the polymer in exposed areas is accelerated by catalyticreaction. In addition, the resist film has a high dissolution contrast,resolution, exposure latitude, and process adaptability, and provides agood pattern profile after exposure, yet better etch resistance, andminimal proximity bias because of restrained acid diffusion. By virtueof these advantages, the composition is fully useful in commercialapplication and suited as a pattern-forming material for the fabricationof VLSIs or photomasks. Particularly when an acid generator isincorporated to formulate a chemically amplified positive resistcomposition capable of utilizing acid catalyzed reaction, thecomposition has a higher sensitivity and is further improved in theproperties described above.

The positive resist composition may further comprise an organic solvent,basic compound, dissolution regulator, surfactant, and acetylenealcohol, alone or in combination. Inclusion of a dissolution regulatormay lead to an increased difference in dissolution rate between exposedand unexposed areas and a further improvement in resolution. Addition ofa basic compound may be effective in suppressing the diffusion rate ofacid in the resist film, achieving a further improvement in resolution.Addition of a surfactant may improve or control the coatingcharacteristics of the resist composition.

The positive resist composition may include an acid generator in orderfor the composition to function as a chemically amplified positiveresist composition. Typical of the acid generator used herein is aphotoacid generator (PAG) capable of generating an acid in response toactinic light or radiation. It is any compound capable of generating anacid upon exposure to high-energy radiation. Suitable PAGs includesulfonium salts, iodonium salts, sulfonyldiazomethane,N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. The acidgenerators may be used alone or in admixture of two or more. Exemplaryacid generators are described in U.S. Pat. No. 7,537,880 (JP-A2008-111103, paragraphs [0122] to [0142]). In the embodiment wherein apolymer having recurring units (d) copolymerized therein is used as thebase resin, the PAG may be omitted.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144] to [0145] (U.S. Pat. No. 7,537,880).Specifically, exemplary solvents include ketones such as cyclohexanoneand methyl-2-n-amyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,tert-butyl propionate, and propylene glycol mono-tert-butyl etheracetate; and lactones such as γ-butyrolactone, and mixtures thereof.Exemplary basic compounds are described in JP-A 2008-111103, paragraphs[0146] to [0164], for example, primary, secondary and tertiary aminecompounds, specifically amine compounds having a hydroxyl, ether, ester,lactone, cyano or sulfonate group. Exemplary surfactants are describedin JP-A 2008-111103, paragraphs [0165] to [0166]. Exemplary dissolutionregulators are described in JP-A 2008-122932 (US 2008090172), paragraphs[0155] to [0178], and exemplary acetylene alcohols in paragraphs [0179]to [0182]. Also useful are quenchers of polymer type as described inJP-A 2008-239918. The polymeric quencher segregates at the resistsurface after coating and thus enhances the rectangularity of resistpattern. When a protective film is applied as is often the case in theimmersion lithography, the polymeric quencher is also effective forpreventing any film thickness loss of resist pattern or rounding ofpattern top.

An appropriate amount of the acid generator used is 0.01 to 100 parts,and preferably 0.1 to 80 parts. An appropriate amount of the organicsolvent used is 50 to 10,000 parts, especially 100 to 5,000 parts. Thedissolution regulator may be blended in an amount of 0 to 50 parts,preferably 0 to 40 parts, the basic compound in an amount of 0 to 100parts, preferably 0.001 to 50 parts, and the surfactant in an amount of0 to 10 parts, preferably 0.0001 to 5 parts. All amounts are expressedin parts by weight relative to 100 parts by weight of the base resin.

Process

The positive resist composition, typically chemically amplified positiveresist composition comprising a polymer having acid labile groups offormula (1), an acid generator, and a basic compound in an organicsolvent is used in the fabrication of various integrated circuits.Pattern formation using the resist composition may be performed bywell-known lithography processes. The process generally involvescoating, prebake, exposure, bake (PEB), and development. If necessary,any additional steps may be added.

The positive resist composition is first applied onto a substrate onwhich an integrated circuit is to be formed (e.g., Si, SiO₂, SiN, SiON,TiN, WSi, BPSG, SOG, or organic antireflective coating) or a substrateon which a mask circuit is to be formed (e.g., Cr, CrO, CrON, MoSi, orSiO₂) by a suitable coating technique such as spin coating, rollcoating, flow coating, dip coating, spray coating or doctor coating. Thecoating is prebaked on a hot plate at a temperature of 60 to 150° C. for10 seconds to 30 minutes, preferably 80 to 120° C. for 30 seconds to 20minutes. The resulting resist film is generally 0.1 to 2.0 μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, x-ray, excimer laser light, γ-ray,synchrotron radiation or EUV (soft x-ray), directly or through a mask.The exposure dose is preferably about 1 to 200 mJ/cm², more preferablyabout 10 to 100 mJ/cm², or 0.1 to 100 μC/cm², more preferably 0.5 to 50μC/cm². The resist film is further baked (PEB) on a hot plate at 60 to150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes.

Thereafter the resist film is developed in a developer in the form of anaqueous base solution for 3 seconds to 3 minutes, preferably 5 secondsto 2 minutes by conventional techniques such as dip, puddle or spraytechniques. Suitable developers are 0.1 to 10 wt %, preferably 2 to 10wt %, more preferably 2 to 8 wt % aqueous solutions oftetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide(TEAH), tetrapropylammonium hydroxide (TPAH) and tetrabutylammoniumhydroxide (TBAH). The resist film in the exposed area is dissolved inthe developer whereas the resist film in the unexposed area is notdissolved. In this way, the desired positive pattern is formed on thesubstrate. It is appreciated that the resist composition of theinvention is best suited for micro-patterning using such high-energyradiation as EB, EUV (soft x-ray), x-ray, γ-ray and synchrotronradiation among others.

Although TMAH aqueous solution is generally used as the developer, TEAH,TPAH and TBAH having a longer alkyl chain are effective in inhibitingthe resist film from being swollen during development and thuspreventing pattern collapse. JP 3429592 describes an example using anaqueous TBAH solution for the development of a polymer comprisingrecurring units having an alicyclic structure such as adamantanemethacrylate and recurring units having an acid labile group such ast-butyl methacrylate, the polymer being water repellent due to theabsence of hydrophilic groups.

The TMAH developer is most often used as 2.38 wt % aqueous solution,which corresponds to 0.26N. The TEAH, TPAH, and TBAH aqueous solutionsshould preferably have an equivalent normality. The concentration ofTEAH, TPAH, and TBAH that corresponds to 0.26N is 3.84 wt %, 5.31 wt %,and 6.78 wt %, respectively.

When a pattern with a line size of 32 nm or less is resolved by the EBand EUV lithography, there arises a phenomenon that lines become wavy,lines merge together, and merged lines collapse. It is believed thatthis phenomenon occurs because lines are swollen in the developer andthe thus expanded lines merge together. Since the swollen linescontaining liquid developer are as soft as sponge, they readily collapseunder the stress of rinsing. For this reason, the developer using along-chain alkyl developing agent is effective for preventing film swelland hence, pattern collapse.

Alternatively, a negative tone pattern may be formed by organic solventdevelopment. The organic solvent used as the developer is preferablyselected from 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, phenyl acetate, propyl formate, butyl formate, isobutylformate, amyl formate, isoamyl formate, methyl valerate, methylpentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethylpropionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate,propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyllactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate. Theseorganic solvents may be used alone or in admixture of two or more.

At the end of organic solvent development, the resist film is rinsed. Asthe rinsing liquid, a solvent which is miscible with the developer anddoes not dissolve the resist film is preferred. Suitable solventsinclude alcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12carbon atoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alkanes of 6 to 12 carbonatoms include hexane, heptane, octane, nonane, decane, undecane,dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-amylether, and di-n-hexyl ether. The solvents may be used alone or inadmixture. Besides the foregoing solvents, aromatic solvents may beused, for example, toluene, xylene, ethylbenzene, isopropylbenzene,tert-butylbenzene and mesitylene.

Example

Synthesis Examples, Comparative Synthesis Examples, Examples andComparative Examples are given below for further illustrating theinvention, but they should not be construed as limiting the inventionthereto. Mw is a weight average molecular weight as measured by gelpermeation chromatography (GPC) versus polystyrene standards, and Mw/Mndesignates molecular weight distribution or dispersity. All parts (pbw)are by weight.

Monomer Synthesis

Polymerizable acid-labile compounds within the scope of the inventionwere synthesized as follows.

Monomer Synthesis Example 1 Synthesis of Monomer 1

With stirring and ice cooling, 111 g of triethylamine was added to amixture of 120 g of methacrylic acid chloride, 180 g of5-fluoro-1-methylindan-1-ol, and 1500 g of toluene. The mixture wasstirred at room temperature for 16 hours. By standard aqueous work-upand solvent distillation, a crude product was obtained. It was purifiedby column chromatography, yielding the target compound, designatedMonomer 1.

By the same procedure, Monomers 2 to 8 were synthesized. In thesynthesis of Monomers 5 to 8, the reactant 5-fluoro-1-methylindan-1-olwas replaced by 5-fluoro-1-ethylindan-1-ol for Monomer 5,5-fluoro-1-cyclopropylindan-1-ol for Monomer 6,7-fluoro-1,2,3,4-tetrahydro-1-methylnaphthalen-1-ol for Monomer 7, and5-trifluoromethyl-1-methylindan-1-ol for Monomer 8.

In the synthesis of Monomers 2 to 4, the reaction was replaced by

reaction of 5-fluoro-1-methylindan-1-ol with 5-carboxylicacid-4-oxatricyclo[4.2.1.0^(3,7)]nonan-5-on-2-yl methacrylate forMonomer 2,reaction of 5-fluoro-1-methylindan-1-ol with 4-vinylbenzoic acid forMonomer 3, andreaction of 5-fluoro-1-methylindan-1-ol with 5-vinyl-1-naphthoic acidfor Monomer 4.

PAG monomers 1 to 7 used herein are shown below.

Polymer Synthesis Polymer Synthesis Example 1

A 2-L flask was charged with 7.0 g of Monomer 1, 11.3 g of4-acetoxystyrene, and 40 g of tetrahydrofuran as solvent. The reactorwas cooled to −70° C. in a nitrogen atmosphere, whereupon vacuumevacuation and nitrogen blow were repeated three times. The reactorwarmed up to room temperature whereupon 1.2 g of azobisisobutyronitrile(AIBN) was added as a polymerization initiator. The reactor was heatedat 60° C. and reaction run for 15 hours. The reaction solution wasprecipitated from 1 L of isopropyl alcohol. The white solid wascollected by filtration and dissolved again in a mixture of 100 mL ofmethanol and 200 mL of tetrahydrofuran, to which 10 g of triethylamineand 10 g of water were added. Deprotection reaction of acetyl group wasconducted at 70° C. for 5 hours, followed by neutralization with aceticacid. The reaction solution was concentrated and dissolved in 100 mL ofacetone. By similar precipitation, filtration, and drying at 60° C., awhite polymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 1:4-hydroxystyrene=0.30:0.70

Mw=8,700

Mw/Mn=1.88

This is designated Polymer 1.

Polymer Synthesis Example 2

A 2-L flask was charged with 5.4 g of Monomer 1, 13.7 g of3-hydroxyphenyl methacrylate, and 40 g of tetrahydrofuran as solvent.The reactor was cooled to −70° C. in a nitrogen atmosphere, whereuponvacuum evacuation and nitrogen blow were repeated three times. Thereactor warmed up to room temperature whereupon 1.2 g of AIBN was addedas a polymerization initiator. The reactor was heated at 60° C. andreaction run for 15 hours. The reaction solution was precipitated from 1L of isopropyl alcohol. The white solid was collected by filtration andvacuum dried at 60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 1:3-hydroxyphenyl methacrylate=0.23:0.77

Mw=8,200

Mw/Mn=1.93

This is designated Polymer 2.

Polymer Synthesis Example 3

A 2-L flask was charged with 5.4 g of Monomer 1, 16.8 g of5-hydroxyindan-2-yl methacrylate, and 40 g of tetrahydrofuran assolvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and vacuum dried at 60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 1:5-hydroxyindan-2-yl methacrylate=0.23:0.77

Mw=8,100

Mw/Mn=1.86

This is designated Polymer 3.

Polymer Synthesis Example 4

A 2-L flask was charged with 7.0 g of Monomer 1, 8.7 g of5-hydroxyindan-2-yl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, and 40 gof tetrahydrofuran as solvent. The reactor was cooled to −70° C. in anitrogen atmosphere, whereupon vacuum evacuation and nitrogen blow wererepeated three times. The reactor warmed up to room temperaturewhereupon 1.2 g of AIBN was added as a polymerization initiator. Thereactor was heated at 60° C. and reaction run for 15 hours. The reactionsolution was precipitated from 1 L of isopropyl alcohol. The white solidwas collected by filtration and vacuum dried at 60° C., obtaining awhite polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:5-hydroxyindan-2-yl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate=0.30:0.40:0.30    -   Mw=8,600    -   Mw/Mn=1.81

This is designated Polymer 4.

Polymer Synthesis Example 5

A 2-L flask was charged with 5.4 g of Monomer 1, 1.7 g of indene, 10.8 gof 4-acetoxystyrene, and 40 g of tetrahydrofuran as solvent. The reactorwas cooled to −70° C. in a nitrogen atmosphere, whereupon vacuumevacuation and nitrogen blow were repeated three times. The reactorwarmed up to room temperature whereupon 1.2 g of AIBN was added as apolymerization initiator. The reactor was heated at 60° C. and reactionrun for 15 hours. The reaction solution was precipitated from 1 L ofisopropyl alcohol. The white solid was collected by filtration anddissolved again in a mixture of 100 mL of methanol and 200 mL oftetrahydrofuran, to which 10 g of triethylamine and 10 g of water wereadded. Deprotection reaction of acetyl group was conducted at 70° C. for5 hours, followed by neutralization with acetic acid. The reactionsolution was concentrated and dissolved in 100 mL of acetone. By similarprecipitation, filtration, and drying at 60° C., a white polymer wasobtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 1:indene:4-hydroxystyrene=0.23:0.10:0.67

Mw=7,100

Mw/Mn=1.95

This is designated Polymer 5.

Polymer Synthesis Example 6

A 2-L flask was charged with 6.5 g of Monomer 1, 5.3 g of4-hydroxyphenyl methacrylate, 6.8 g of 4-acetoxystyrene, and 40 g oftetrahydrofuran as solvent. The reactor was cooled to −70° C. in anitrogen atmosphere, whereupon vacuum evacuation and nitrogen blow wererepeated three times. The reactor warmed up to room temperaturewhereupon 1.2 g of AIBN was added as a polymerization initiator. Thereactor was heated at 60° C. and reaction run for 15 hours. The reactionsolution was precipitated from 1 L of isopropyl alcohol. The white solidwas collected by filtration and dissolved again in a mixture of 100 mLof methanol and 200 mL of tetrahydrofuran, to which 10 g oftriethylamine and 10 g of water were added. Deprotection reaction ofacetyl group was conducted at 70° C. for 5 hours, followed byneutralization with acetic acid. The reaction solution was concentratedand dissolved in 100 mL of acetone. By similar precipitation,filtration, and drying at 60° C., a white polymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:4-hydroxyphenyl        methacrylate:4-hydroxystyrene=0.28:0.30:0.42

Mw=7,600

Mw/Mn=1.74

This is designated Polymer 6.

Polymer Synthesis Example 7

A 2-L flask was charged with 6.1 g of Monomer 1, 6.8 g of1-hydroxynaphthalen-5-yl methacrylate, 7.5 g oftetrahydro-2-oxofuran-3-yl methacrylate, and 40 g of tetrahydrofuran assolvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and vacuum dried at 60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:1-hydroxynaphthalen-5-yl        methacrylate:tetrahydro-2-oxofuran-3-yl        methacrylate=0.26:0.30:0.44

Mw=8,600

Mw/Mn=1.83

This is designated Polymer 7.

Polymer Synthesis Example 8

A 2-L flask was charged with 5.4 g of Monomer 1, 10.7 g of4-acetoxystyrene, 1.7 g of acenaphthylene, and 20 g of tetrahydrofuranas solvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and dissolved again in a mixture of 100 mL of methanol and200 mL of tetrahydrofuran, to which 10 g of triethylamine and 10 g ofwater were added. Deprotection reaction of acetyl group was conducted at70° C. for 5 hours, followed by neutralization with acetic acid. Thereaction solution was concentrated and dissolved in 100 mL of acetone.By similar precipitation, filtration, and drying at 60° C., a whitepolymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:4-hydroxystyrene:acenaphthylene=0.23:0.67:0.10

Mw=6,200

Mw/Mn=1.83

This is designated Polymer 8.

Polymer Synthesis Example 9

A 2-L flask was charged with 5.6 g of Monomer 1, 2.0 g of7-acetoxyindene, 10.6 g of 4-acetoxystyrene, and 40 g of tetrahydrofuranas solvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and dissolved again in a mixture of 100 mL of methanol and200 mL of tetrahydrofuran, to which 10 g of triethylamine and 10 g ofwater were added. Deprotection reaction of acetyl group was conducted at70° C. for 5 hours, followed by neutralization with acetic acid. Thereaction solution was concentrated and dissolved in 100 mL of acetone.By similar precipitation, filtration, and drying at 60° C., a whitepolymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:7-hydroxyindene:4-hydroxystyrene=0.24:0.10:0.66    -   Mw=6,100    -   Mw/Mn=1.72

This is designated Polymer 9.

Polymer Synthesis Example 10

A 2-L flask was charged with 5.4 g of Monomer 1, 8.3 g of4-acetoxystyrene, 2.7 g of 6-hydroxycoumarin, 1.5 g of coumarin, and 20g of tetrahydrofuran as solvent. The reactor was cooled to −70° C. in anitrogen atmosphere, whereupon vacuum evacuation and nitrogen blow wererepeated three times. The reactor warmed up to room temperaturewhereupon 1.2 g of AIBN was added as a polymerization initiator. Thereactor was heated at 60° C. and reaction run for 15 hours. The reactionsolution was precipitated from 1 L of isopropyl alcohol. The white solidwas collected by filtration and dissolved again in a mixture of 100 mLof methanol and 200 mL of tetrahydrofuran, to which 10 g oftriethylamine and 10 g of water were added. Deprotection reaction ofacetyl group was conducted at 70° C. for 5 hours, followed byneutralization with acetic acid. The reaction solution was concentratedand dissolved in 100 mL of acetone. By similar precipitation,filtration, and drying at 60° C., a white polymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer        1:4-hydroxystyrene:6-hydroxycoumarin:coumarin=0.23:0.52:0.15:0.10    -   Mw=6,600    -   Mw/Mn=1.98

This is designated Polymer 10.

Polymer Synthesis Example 11

A 2-L flask was charged with 5.4 g of Monomer 1, 15.5 g of5-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl methacrylate, 1.6 g ofchromone, and 20 g of tetrahydrofuran as solvent. The reactor was cooledto −70° C. in a nitrogen atmosphere, whereupon vacuum evacuation andnitrogen blow were repeated three times. The reactor warmed up to roomtemperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:5-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl        methacrylate:chromone=0.23:0.67:0.10    -   Mw=6,400    -   Mw/Mn=1.61

This is designated Polymer 11.

Polymer Synthesis Example 12

A 2-L flask was charged with 6.8 g of Monomer 3, 10.7 g of4-acetoxystyrene, 1.6 g of chromone, and 20 g of tetrahydrofuran assolvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and dissolved again in a mixture of 100 mL of methanol and200 mL of tetrahydrofuran, to which 10 g of triethylamine and 10 g ofwater were added. Deprotection reaction of acetyl group was conducted at70° C. for 5 hours, followed by neutralization with acetic acid. Thereaction solution was concentrated and dissolved in 100 mL of acetone.By similar precipitation, filtration, and drying at 60° C., a whitepolymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 3:4-hydroxystyrene:chromone=0.23:0.67:0.10

Mw=8,500

Mw/Mn=1.75

This is designated Polymer 12.

Polymer Synthesis Example 13

A 2-L flask was charged with 8.0 g of Monomer 4, 10.4 g of4-acetoxystyrene, 1.8 g of coumarin, and 20 g of tetrahydrofuran assolvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and dissolved again in a mixture of 100 mL of methanol and200 mL of tetrahydrofuran, to which 10 g of triethylamine and 10 g ofwater were added. Deprotection reaction of acetyl group was conducted at70° C. for 5 hours, followed by neutralization with acetic acid. Thereaction solution was concentrated and dissolved in 100 mL of acetone.By similar precipitation, filtration, and drying at 60° C., a whitepolymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 4:4-hydroxystyrene:coumarin=0.23:0.65:0.12

Mw=7,600

Mw/Mn=1.75

This is designated Polymer 13.

Polymer Synthesis Example 14

A 2-L flask was charged with 7.0 g of Monomer 1, 5.3 g of4-hydroxyphenyl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 6.5 g ofPAG monomer 1, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 1=0.30:0.30:0.30:0.10    -   Mw=8,300    -   Mw/Mn=1.81

This is designated Polymer 14.

Polymer Synthesis Example 15

A 2-L flask was charged with 7.0 g of Monomer 1, 5.3 g of4-hydroxyphenyl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.7 g ofPAG monomer 2, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 2=0.30:0.30:0.30:0.10    -   Mw=8,100    -   Mw/Mn=1.61

This is designated Polymer 15.

Polymer Synthesis Example 16

A 2-L flask was charged with 7.0 g of Monomer 1, 5.3 g of4-hydroxyphenyl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.30:0.30:0.10    -   Mw=7,200    -   Mw/Mn=1.77

This is designated Polymer 16.

Polymer Synthesis Example 17

A 2-L flask was charged with 3.5 g of Monomer 1, 4.1 g of3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl methacrylate,5.4 g of 3-hydroxyphenyl methacrylamide, 6.5 g of2,7-dihydro-2-oxobenzo[C]furan-5-yl methacrylate, 5.6 g of PAG monomer3, and 40 g of tetrahydrofuran as solvent. The reactor was cooled to−70° C. in a nitrogen atmosphere, whereupon vacuum evacuation andnitrogen blow were repeated three times. The reactor warmed up to roomtemperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer        1:3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]-dodecanyl        methacrylate:3-hydroxyphenyl        methacrylamide:2,7-dihydro-2-oxobenzo[C]furan-5-yl        methacrylate:PAG monomer 3=0.15:0.15:0.30:0.30:0.10    -   Mw=7,600    -   Mw/Mn=1.74

This is designated Polymer 17.

Polymer Synthesis Example 18

A 2-L flask was charged with 7.0 g of Monomer 1, 6.4 g of6-acetoxy-2-vinylnaphthalene, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and dissolved againin a mixture of 100 mL of methanol and 200 mL of tetrahydrofuran, towhich 10 g of triethylamine and 10 g of water were added. Deprotectionreaction of acetyl group was conducted at 70° C. for 5 hours, followedby neutralization with acetic acid. The reaction solution wasconcentrated and dissolved in 100 mL of acetone. By similarprecipitation, filtration, and drying at 60° C., a white polymer wasobtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer        1:6-hydroxy-2-vinylnaphthalene:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.30:0.30:0.10    -   Mw=8,900    -   Mw/Mn=1.89

This is designated Polymer 18.

Polymer Synthesis Example 19

A 2-L flask was charged with 7.0 g of Monomer 1, 6.5 g of5-hydroxyindan-2-yl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:5-hydroxyindan-2-yl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.30:0.30:0.10    -   Mw=7,700    -   Mw/Mn=1.66

This is designated Polymer 19.

Polymer Synthesis Example 20

A 2-L flask was charged with 7.0 g of Monomer 1, 7.4 g of5,8-dihydroxy-1,2,3,4-tetrahydronaphthalen-2-yl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]-nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:5,8-dihydroxy-1,2,3,4-tetrahydronaphthalen-2-yl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]-nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.20:0.40:0.10    -   Mw=7,600    -   Mw/Mn=1.79

This is designated Polymer 20.

Polymer Synthesis Example 21

A 2-L flask was charged with 7.0 g of Monomer 1, 7.4 g of6-hydroxycoumarin-3-yl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:6-hydroxycoumarin-3-yl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.20:0.40:0.10    -   Mw=8,100    -   Mw/Mn=1.89

This is designated Polymer 21.

Polymer Synthesis Example 22

A 2-L flask was charged with 12.4 g of Monomer 2, 5.4 g of2-hydroxypyridin-6-yl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 2:2-hydroxypyridin-6-yl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.30:0.30:0.10    -   Mw=8,300    -   Mw/Mn=1.75

This is designated Polymer 22.

Polymer Synthesis Example 23

A 2-L flask was charged with 7.4 g of Monomer 5, 4.5 g of4-hydroxy-1-naphthalene methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 5:4-hydroxy-1-naphthalene        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.20:0.40:0.10    -   Mw=7,500    -   Mw/Mn=1.75

This is designated Polymer 23.

Polymer Synthesis Example 24

A 2-L flask was charged with 7.8 g of Monomer 6, 5.3 g of4-hydroxyphenyl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 6:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.30:0.30:0.10    -   Mw=7,600    -   Mw/Mn=1.95

This is designated Polymer 24.

Polymer Synthesis Example 25

A 2-L flask was charged with 7.4 g of Monomer 7, 5.3 g of4-hydroxyphenyl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g ofPAG monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 7:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.30:0.30:0.10    -   Mw=7,300    -   Mw/Mn=1.93

This is designated Polymer 25.

Polymer Synthesis Example 26

A 2-L flask was charged with 3.5 g of Monomer 1, 3.4 g of3-ethyl-3-cyclooctane methacrylate, 5.3 g of 4-hydroxyphenylmethacrylate, 6.5 g of 2,7-dihydro-2-oxobenzo[C]furan-5-yl methacrylate,5.6 g of PAG monomer 4, and 40 g of tetrahydrofuran as solvent. Thereactor was cooled to −70° C. in a nitrogen atmosphere, whereupon vacuumevacuation and nitrogen blow were repeated three times. The reactorwarmed up to room temperature whereupon 1.2 g of AIBN was added as apolymerization initiator. The reactor was heated at 60° C. and reactionrun for 15 hours. The reaction solution was precipitated from 1 L ofisopropyl alcohol. The white solid was collected by filtration andvacuum dried at 60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:3-ethyl-3-cyclooctane methacrylate:4-hydroxyphenyl        methacrylate:2,7-dihydro-2-oxobenzo[C]furan-5-yl        methacrylate:PAG monomer 4=0.15:0.15:0.30:0.30:0.10    -   Mw=7,600    -   Mw/Mn=1.71

This is designated Polymer 26.

Polymer Synthesis Example 27

A 2-L flask was charged with 7.1 g of Monomer 8, 2.0 g of4-amyloxystyrene, 5.3 g of 4-hydroxyphenyl methacrylate, 6.7 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.7 g ofPAG monomer 5, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and vacuum dried at60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 8:4-amyloxystyrene:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 5=0.20:0.10:0.30:0.30:0.10    -   Mw=7,600    -   Mw/Mn=1.96

This is designated Polymer 27.

Polymer Synthesis Example 28

A 2-L flask was charged with 5.9 g of Monomer 1, 2.3 g of4-t-butoxyphenyl methacrylate, 5.3 g of 4-hydroxyphenyl methacrylate,6.7 g of 3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]-nonan-9-yl methacrylate,7.4 g of PAG monomer 6, and 40 g of tetrahydrofuran as solvent. Thereactor was cooled to −70° C. in a nitrogen atmosphere, whereupon vacuumevacuation and nitrogen blow were repeated three times. The reactorwarmed up to room temperature whereupon 1.2 g of AIBN was added as apolymerization initiator. The reactor was heated at 60° C. and reactionrun for 15 hours. The reaction solution was precipitated from 1 L ofisopropyl alcohol. The white solid was collected by filtration andvacuum dried at 60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:4-t-butoxyphenyl methacrylate:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 6=0.20:0.10:0.30:0.30:0.10    -   Mw=7,300    -   Mw/Mn=1.93

This is designated Polymer 28.

Polymer Synthesis Example 29

A 2-L flask was charged with 4.7 g of Monomer 1, 3.5 g of3-cyclohexyl-3-cyclopentane methacrylate, 4.3 g of 4-hydroxyphenylmethacrylate, 6.7 g of 3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-ylmethacrylate, 6.7 g of PAG monomer 7, and 40 g of tetrahydrofuran assolvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and vacuum dried at 60° C., obtaining a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   Monomer 1:3-cyclohexyl-3-cyclopentane        methacrylate:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 7=0.20:0.15:0.25:0.30:0.10    -   Mw=7,400    -   Mw/Mn=1.71

This is designated Polymer 29.

Comparative Synthesis Example 1

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   hydroxystyrene:1-ethylcyclopentyl methacrylate=0.70:0.30    -   Mw=9,300    -   Mw/Mn=1.86

This is designated Comparative Polymer 1.

Comparative Synthesis Example 2

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   hydroxystyrene:1-dimethylphenyl methacrylate=0.67:0.33    -   Mw=8,300    -   Mw/Mn=1.97

This is designated Comparative Polymer 2.

Comparative Synthesis Example 3

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   hydroxystyrene:2-(naphthalene-3-yl)propan-2-yl        methacrylate=0.72:0.28    -   Mw=8,600    -   Mw/Mn=1.91

This is designated Comparative Polymer 3.

Comparative Synthesis Example 4

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

hydroxystyrene:1-phenylethyl methacrylate=0.65:0.35

Mw=8,300

Mw/Mn=1.97

This is designated Comparative Polymer 4.

Comparative Synthesis Example 5

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   hydroxystyrene:tetrahydronaphthalen-1-yl methacrylate=0.70:0.30    -   Mw=7,200    -   Mw/Mn=1.71

This is designated Comparative Polymer 5.

Comparative Synthesis Example 6

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

hydroxystyrene:indan-1-yl methacrylate=0.70:0.30

Mw=7,300

Mw/Mn=1.79

This is designated Comparative Polymer 6.

Comparative Synthesis Example 7

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   hydroxystyrene:1-methylindan-1-yl methacrylate=0.70:0.30    -   Mw=7,600    -   Mw/Mn=1.73

This is designated Comparative Polymer 7.

Comparative Synthesis Example 8

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   1-ethylcyclopentyl methacrylate:4-hydroxyphenyl        methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl        methacrylate:PAG monomer 3=0.30:0.30:0.30:0.10    -   Mw=7,900    -   Mw/Mn=1.89

This is designated Comparative Polymer 8.

Examples and Comparative Examples

Positive resist compositions were prepared by dissolving each of thepolymers synthesized above and selected components in a solvent inaccordance with the recipe shown in Tables 1 and 2, and filteringthrough a filter having a pore size of 0.2 μm. The solvent contained 100ppm of a surfactant FC-4430 (3M Sumitomo Co., Ltd.).

The components in Tables 1 and 2 are as identified below.

-   Polymers 1 to 29: polymers synthesized in Polymer Synthesis Examples    1 to 29-   Comparative Polymers 1 to 8:    -   polymers synthesized in Comparative Synthesis Examples 1 to 8-   Organic solvents: propylene glycol monomethyl ether acetate (PGMEA)    -   cyclohexanone (CyH)-   Acid generators: PAG1 and PAG2 of the following structural formulae

-   Basic compounds: Amine 1, Amine 2, and Amine 3 of the following    structural formulae

-   Dissolution regulators:    -   DRI1 and DRI2 of the following structural formulae

EB Writing Test

Using a coater/developer system Clean Track Mark 5 (Tokyo ElectronLtd.), the positive resist composition prepared above was spin coatedonto a silicon substrate (diameter 6 inches, vapor primed withhexamethyldisilazane (HMDS)) and pre-baked on a hot plate at 110° C. for60 seconds to form a resist film of 100 nm thick. Using a system HL-800D(Hitachi Ltd.) at a HV voltage of 50 keV, the resist film was exposedimagewise to EB in a vacuum chamber.

Using Clean Track Mark 5, immediately after the imagewise exposure, thewafer was baked (PEB) on a hot plate for 60 seconds and puddle developedin a 2.38 wt % TMAH aqueous solution for 30 seconds to form a positivepattern.

Resolution is a minimum size at the exposure dose (sensitivity) thatprovides a 1:1 resolution of a 120-nm line-and-space pattern. The 120-nmline-and-space pattern was measured for line width roughness (LWR) underSEM.

The resist composition is shown in Tables 1 and 2 together with thesensitivity and resolution of EB lithography.

TABLE 1 Acid Dissolution Organic PEB Polymer generator Base regulatorsolvent temperature Sensitivity Resolution LWR (pbw) (pbw) (pbw) (pbw)(pbw) (° C.) (μC/cm²) (nm) (nm) Polymer 1 PAG 2 Amine 1 — PGMEA 85 26 857.0 (100) (10) (1.5) (2,000) Polymer 2 PAG 2 Amine 1 — PGMEA 85 31 857.0 (100) (10) (1.5) (2,000) Polymer 3 PAG 2 Amine 1 — PGMEA 85 34 857.0 (100) (10) (1.5) (2,000) Polymer 4 PAG 2 Amine 1 — PGMEA 85 39 857.2 (100) (10) (1.5) (2,000) Polymer 5 PAG 1 Amine 1 — PGMEA 85 31 856.9 (100) (10) (1.5) (2,000) Polymer 6 PAG 1 Amine 1 — PGMEA 85 34 856.3 (100) (10) (1.5) (2,000) Polymer 7 PAG 1 Amine 1 — PGMEA 85 34 856.4 (100) (10) (1.5) (2,000) Polymer 8 PAG 1 Amine 1 — PGMEA 85 34 856.5 (100) (10) (1.5) (2,000) Polymer 9 PAG 1 Amine 1 — PGMEA 85 33 856.6 (100) (10) (1.5) (2,000) Polymer 10 PAG 1 Amine 1 — PGMEA 85 33 856.0 (100) (10) (1.5) (2,000) Polymer 11 PAG 1 Amine 1 — PGMEA 85 38 856.0 (100) (10) (1.5) (2,000) Polymer 12 PAG 2 Amine 1 — PGMEA 85 38 907.2 (100) (10) (1.5) (2,000) Polymer 13 PAG 1 Amine 1 — PGMEA 85 40 908.0 (100) (10) (1.5) (2,000) Polymer 14 — Amine 1 — PGMEA (500) 85 40 805.2 (100) (1.5) CyH (1,500) Polymer 15 — Amine 1 — PGMEA (500) 85 40 825.0 (100) (1.5) CyH (1,500) Polymer 16 — Amine 1 — PGMEA (500) 85 36 754.3 (100) (1.5) CyH (1,500) Polymer 17 — Amine 1 — PGMEA (500) 85 34 754.4 (100) (1.5) CyH (1,500) Polymer 18 — Amine 1 — PGMEA (500) 85 35 705.0 (100) (1.5) CyH (1,500) Polymer 19 — Amine 1 — PGMEA (500) 85 34 654.7 (100) (1.5) CyH (1,500) Polymer 20 — Amine 1 — PGMEA (500) 85 33 704.5 (100) (1.5) CyH (1,500) Polymer 21 — Amine 1 — PGMEA (500) 85 38 704.1 (100) (1.5) CyH (1,500) Polymer 22 — Amine 1 — PGMEA (500) 85 39 704.4 (100) (1.5) CyH (1,500) Polymer 23 — Amine 1 — PGMEA (500) 80 39 704.3 (100) (1.5) CyH (1,500) Polymer 24 — Amine 1 — PGMEA (500) 75 37 704.1 (100) (1.5) CyH (1,500) Polymer 25 — Amine 1 — PGMEA (500) 85 39 704.1 (100) (1.5) CyH (1,500) Polymer 26 — Amine 1 — PGMEA (500) 70 37 654.1 (100) (1.5) CyH (1,500)

TABLE 2 Acid Dissolution Organic PEB Polymer generator Base regulatorsolvent temperature Sensitivity Resolution LWR (pbw) (pbw) (pbw) (pbw)(pbw) (° C.) (μC/cm²) (nm) (nm) Polymer 27 — Amine 1 — PGMEA (500) 80 4165 4.2 (100) (1.5) CyH (1,500) Polymer 28 — Amine 1 — PGMEA (500) 85 3865 4.2 (100) (1.5) CyH (1,500) Polymer 16 — Amine 2 — PGMEA (500) 85 4375 4.3 (100) (0.5) CyH (1,500) Polymer 16 — Amine 3 — PGMEA (500) 85 4575 4.4 (100) (0.7) CyH (1,500) Polymer 16 — Amine 1 DRI 1 PGMEA (500) 8531 80 4.1 (100) (1.5) (10) CyH (1,500) Polymer 16 — Amine 1 DRI 2 PGMEA(500) 85 34 80 4.1 (100) (1.5) (10) CyH (1,500) Polymer 29 — Amine 1 —PGMEA (500) 85 40 80 4.5 (100) (1.5) CyH (1,500) Comparative PAG 2 Amine1 — PGMEA 90 25 110 7.2 Polymer 1 (10) (1.5) (2,000) (100) ComparativePAG 2 Amine 1 — PGMEA 80 30 120 7.9 Polymer 2 (10) (1.5) (2,000) (100)Comparative PAG 2 Amine 1 — PGMEA 80 45 100 8.8 Polymer 3 (10) (1.5)(2,000) (100) Comparative PAG 2 Amine 1 — PGMEA 95 55 95 8.5 Polymer 4(10) (1.5) (2,000) (100) Comparative PAG 2 Amine 1 — PGMEA 90 42 95 7.9Polymer 5 (10) (1.5) (2,000) (100) Comparative PAG 2 Amine 1 — PGMEA 9045 95 8.2 Polymer 6 (10) (1.5) (2,000) (100) Comparative PAG 2 Amine 1 —PGMEA 80 32 95 7.9 Polymer 7 (10) (1.5) (2,000) (100) Comparative —Amine 1 — PGMEA(500) 90 52 80 5.3 Polymer 8 (1.5) CyH(1,500) (100)

Dry Etching Test

Each polymer, 2 g, was thoroughly dissolved in 10 g of cyclohexanone,and passed through a filter having a pore size of 0.2 μm, obtaining apolymer solution. The polymer solution was spin coated onto a siliconsubstrate and baked to form a polymer film of 300 nm thick. Using a dryetching instrument TE-8500P (Tokyo Electron Ltd.), the polymer film wasetched with CHF₃/CF₄ gas under the following conditions.

Chamber pressure 40.0 Pa RF power 1000 W Gap 9 mm CHF₃ gas flow rate 30ml/min CF₄ gas flow rate 30 ml/min Ar gas flow rate 100 ml/min Time 60sec

The difference in polymer film thickness before and after etching wasdetermined, from which an etching rate per minute was computed. Theresults are shown in Table 3. A smaller value of film thicknessdifference, i.e., a lower etching rate indicates better etchingresistance.

TABLE 3 CHF₃/CF₄ gas etching rate (nm/min) Polymer 1 95 Polymer 2 103Polymer 3 103 Polymer 4 107 Polymer 5 94 Polymer 6 103 Polymer 7 100Polymer 8 91 Polymer 9 94 Polymer 10 95 Polymer 11 95 Polymer 12 94Polymer 13 84 Polymer 14 94 Polymer 15 97 Polymer 16 98 Polymer 17 96Polymer 18 92 Polymer 19 91 Polymer 20 98 Polymer 21 100 Polymer 22 101Polymer 23 98 Polymer 24 96 Polymer 25 96 Polymer 26 95 Polymer 27 93Polymer 28 92 Polymer 29 91 Comparative Polymer 1 122 ComparativePolymer 2 110 Comparative Polymer 3 95 Comparative Polymer 4 111Comparative Polymer 5 100 Comparative Polymer 6 103 Comparative Polymer7 111 Comparative Polymer 8 116

It is evident from Tables 1 and 2 that the resist compositions using theinventive polymers show satisfactory resolution, sensitivity and edgeroughness. Although some polymers comprising an acid generator ofpolymer type copolymerized therein and having conventional acid labilegroups are drastically improved in resolution and edge roughnessproperties and sometimes superior to those polymers which do not containan acid generator of polymer type, but fall within the scope of theinvention, the polymers having acid labile groups within the scope ofthe invention and comprising an acid generator copolymerized thereinexhibit excellent resolution and minimized edge roughness owing to theirsynergy. These polymers have good dry etching resistance as demonstratedby a smaller difference in film thickness before and after etching inTable 3.

Japanese Patent Application No. 2011-218939 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A positive resist composition comprising as a base resin a polymerhaving carboxyl groups whose hydrogen is substituted by an acid labilegroup having the general formula (1):

wherein R¹ is methylene or ethylene, R² is a straight, branched orcyclic C₁-C₈ alkyl, C₆-C₁₀ aryl, or C₂-C₁₀ alkenyl group, which maycontain an oxygen or sulfur atom, R³ is fluorine or trifluoromethyl, andm is an integer of 1 to
 4. 2. The resist composition of claim 1,comprising as the base resin a polymer comprising recurring units (a) ofthe general formula (2), selected from (meth)acrylic acid andderivatives thereof, styrenecarboxylic acid, andvinylnaphthalenecarboxylic acid, each having substituted thereon an acidlabile group of formula (1), the polymer having a weight averagemolecular weight of 1,000 to 500,000,

wherein R¹ to R³, and m are as defined above, X¹ is a single bond,—C(═O)—O—R⁵—, phenylene or naphthylene group, R⁵ is a straight, branchedor cyclic C₁-C₁₀ alkylene group which may have an ester radical, etherradical or lactone ring, and R⁴ is hydrogen or methyl.
 3. The resistcomposition of claim 2 wherein said polymer is a copolymer comprisingrecurring units (a) of the general formula (2), selected from(meth)acrylic acid and derivatives thereof, styrenecarboxylic acid, andvinylnaphthalenecarboxylic acid, each having substituted thereon an acidlabile group of formula (1), and recurring units (b) having an adhesivegroup selected from the class consisting of hydroxyl, lactone, ether,ester, carbonyl, cyano, sulfonic acid ester, sulfonamide groups, cyclic—O—C(═O)—S— and —O—C(═O)—NH— groups, molar fractions “a” and “b” of therespective units being in the range: 0<a<1.0, 0<b<1.0, and 0.05≦a+b≦1.0,the copolymer having a weight average molecular weight of 1,000 to500,000.
 4. The resist composition of claim 3 wherein the recurringunits (b) are recurring units having a phenolic hydroxyl group.
 5. Theresist composition of claim 4 wherein the recurring units having aphenolic hydroxyl group are selected from units (b1) to (b9) representedby the following general formula (3):

wherein Y¹, Y² and Y⁵ each are a single bond or —C(═O)—O—R²¹—, Y³ and Y⁴each are —C(═O)—O—R²²—, R²¹ and R²² each are a single bond or astraight, branched or cyclic C₁-C₁₀ alkylene group which may contain anether or ester radical, R²⁰ is each independently hydrogen or methyl, Z¹and Z² each are methylene or ethylene, Z³ is methylene, oxygen orsulfur, Z⁴ and Z⁵ each are CH or nitrogen, and p is 1 or
 2. 6. Theresist composition of claim 3 wherein the copolymer has furthercopolymerized therein recurring units selected from units (c1) to (c5)of indene, acenaphthylene, chromone, coumarin, and norbornadiene, orderivatives thereof, represented by the following general formula (4):

wherein R²³ to R²⁷ are each independently selected from the classconsisting of hydrogen, C₁-C₃₀ alkyl, partially or entirelyhalo-substituted alkyl, alkoxy, alkanoyl or alkoxycarbonyl group, C₆-C₁₀aryl group, halogen, and 1,1,1,3,3,3-hexafluoro-2-propanol, and W¹ ismethylene, oxygen or sulfur.
 7. The resist composition of claim 3wherein the copolymer has further copolymerized therein units selectedfrom sulfonium salts (d1) to (d3) represented by the following generalformula (5):

wherein R³⁰, R³⁴, and R³⁸ each are hydrogen or methyl, R³¹ is a singlebond, phenylene, —O—R⁴²—, or —C(═O)—Y¹⁰—R⁴²—, Y¹⁰ is oxygen or NH, R⁴²is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylene orphenylene group, which may contain a carbonyl, ester, ether or hydroxylradical, R³², R³³, R³⁵, R³⁶, R³⁷, R³⁹, R⁴⁰, and R⁴¹ are eachindependently a straight, branched or cyclic C₁-C₁₂ alkyl group whichmay contain a carbonyl, ester or ether radical, or a C₆-C₁₂ aryl, C₇-C₂₀aralkyl, or thiophenyl group, Z¹⁰ is a single bond, methylene, ethylene,phenylene, fluorophenylene, —O—R⁴³—, or —C(═O)—Z¹¹—R⁴³—, Z¹¹ is oxygenor NH, R⁴³ is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene or phenylene group, which may contain a carbonyl, ester,ether or hydroxyl radical, M⁻ is a non-nucleophilic counter ion, d1, d2and d3 are in the range of 0≦d1≦0.3, 0≦d2≦0.3, 0≦d3≦0.3, and0<d1+d2+d3≦0.3.
 8. The resist composition of claim 1, further comprisingan organic solvent and an acid generator, the composition being achemically amplified positive resist composition.
 9. The resistcomposition of claim 8, further comprising a dissolution regulator. 10.The resist composition of claim 8, further comprising a basic compoundand/or a surfactant as an additive.
 11. A pattern forming processcomprising the steps of applying the positive resist composition of anyone of claims 1 to 10 onto a substrate to form a coating, baking,exposing the coating to high-energy radiation, and developing theexposed coating in a developer.